CRF's Only Forums

Hello everyone, this is my first post on CRF's only and I need y'all's help. I am going to to be going to New Mexico for a three day ride at the end of this month, and the altitude of Rio Rancho, is around 5,200 ft, while where I normally ride in Arizona is around 1,200. So naturally I really need to change my jets.

Bike: 2004 CRF450R

Here's a list of mod's done to my bike's powerplant:
Athena 500cc big bore kit
Wiseco 101mm (5.0+) 12.5:1 piston
Kibblewhite stainless steel valves
WebCam Mysto camshaft
Ported head and ported carb
Oversized intake and exhaust valves (+1 or 2 iirc)
Stainless steel header tuned by Dynojet (Stage 3)
FMF Titanium muffler
Hinson Full Clutch kit (I can't remember if it was the Billetproof or Momentum)
Trail Tech flywheel
Vortex Programmable CDI box
JD jetting kit
NGK IFR9 Spark plug
Uni are filter
12T Front, 48T Rear 520 chain
I run a 21in front wheel and 19in rear

For oil I run Bel Ray's EXP Synthetic Ester at 10w40.

What do you guys recommend that I use for taking this bike to NM? It will be the highest altitude the bike has ever seen. Thank you guys for all the help.

In winter temps, a 158 main. Leave everything else alone. The main is only for wide open throttle or close to it anyway. in summer, a 155.

Big bores usually require a leaner main. I know that sounds backwards. An engine is an air pump, and a more efficient air pump with higher compression, porting, more cc's pulls more fuel through any given jet.

In winter temps, a 158 main. Leave everything else alone. The main is only for wide open throttle or close to it anyway. in summer, a 155.

Big bores usually require a leaner main. I know that sounds backwards. An engine is an air pump, and a more efficient air pump with higher compression, porting, more cc's pulls more fuel through any given jet.

So I should leave everything else alone even though it's dialed in for 1500 feet? I presume that would mean just changing the main and then fine tuning with my air fuel mixture?

Yes, that is a perfectly good starting point, and you may not have to touch it.
These bikes run pretty well when the jetting is way off, and you will be way close.